1. Field
The following description relates to an image reconstruction method and apparatus, and a medical image system employing the image reconstruction method and apparatus.
2. Description of the Related Art
X-ray mammography is widely used to process an image of an internal organ, for example, to process an image of breast tissues. For example, a Full Field Digital Mammography (FFDM) is believed by some as a cost effective approach to detect a microcalcification tissue with an extremely small size. In X-ray mammography, however, performance may be degraded when detecting a mass that is one of main lesions. In the case of breast examination, a radiation image for a breast may be obtained by compressing tissues in the breast, and by performing two-dimensional (2D) projection. Here, however, when a density is high, it may be difficult to perform an accurate diagnosis, since a large number of tissues appear to overlap each other.
A Digital Breast Tomosynthesis (DBT) scheme may be used to capture an object to be inspected, for example, a breast, from 7 to 30 different angles, in a different manner from the X-ray mammography. Thus, the DBT scheme may improve the overlapping of tissues issue.
A Computerized Tomography (CT) scheme may enable a three-dimensional (3D) reconstruction, since projection data for an angle greater than 180° is obtained. Here, a Filtered Back-Projection (FBP) may be used as a reconstruction algorithm, and simple filtering is performed in the Fourier domain and a back projection for combination in an image domain is performed.
In a tomographic image, that is, an image acquired under a tomosynthesis scheme, information may be lost as images are acquired in a limited angle range.
A large number of X-ray systems display an image using a detected attenuation characteristic by passing an X-ray with a single energy band through an object to be inspected. When materials of the object have different attenuation characteristics, an image in high quality may be obtained. However, when the materials of the object have similar attenuation characteristics, the quality of the image may be deteriorated.
A multi-energy X-ray based system may acquire an X-ray image with at least two energy bands. Generally, since materials exhibit different X-ray attenuation characteristics in different energy bands, images may be discriminated for each material based on the different X-ray attenuation characteristics.
Currently, with regards to CT schemes or nondestructive inspection devices, products equipped with a dual energy source or a dual energy separation detector are being launched. The products may acquire an image by rotating a source by at least 180° on an object to be inspected and accordingly, it is possible to obtain density images of materials forming the object. A dual energy CT equipment may be used to obtain an image with a constant quality in a relatively simple manner, for example, by masking Pseudo-color by adding, subtracting, or segmenting an acquired image.
In 3D reconstruction, a beam hardening artifact may occur due to approximation of monochromatic radiation. An inner portion of an object to be inspected may appear abnormally dark due to the beam hardening artifact. In other words, reconstruction is performed by more considerable attenuations in an outer portion of the object, and thus the dark inner portion of the object may be interpreted as a phenomenon due to approximation of monochromatic radiation.
As described above, a system associated with a multi-energy X-ray using at least two different energy spectrums has been proposed. In reconstruction using the system, approximation of monochromatic radiation may be used.